The intraocular lens is broadly used in the treatment of cataracts. The frequency of use of pseudophakos is steadily increasing with the increasing number of patients with senile cataracts; the quality of intraocular lenses (hereinafter, referred to sometimes as "IOL") has also been much improved.
However, in cases of surgery for IOL implantation, the proteins contained in the blood derived from intraoperative bleeding or in postoperative exudates may deposit on the intraocular lens, which is made of an artificial material, so that complete recovery of vision cannot be obtained in some instances. Particularly, the fibrinogen contained in the blood and exudates is activated by the IOL and the resulting insoluble fibrin not only opacifies the lens, but also favors deposition of fibroblasts and other matter on the lens surface, because of its cell adhesion property; this detracts from the designed performance characteristics of the implanted IOL.
Therefore, attempts have been made to provide intraocular lenses made of a variety of hydrophilic materials, such as, poly(2-hydroxyethyl methacrylate) (RINGAN, Vol. 42, No. 6pp. 618-621(June, 1988)), or to subject the IOL to surface treatment with a hydrophilic substance. However, although such materials and substances are capable of reducing the adsorption of blood-derived proteins and the like, their effect is not fully satisfactory. Moreover, even lenses made of these new materials are not completely free from the above-mentioned problems of the deposition of insoluble fibrin originating from the blood and exudates associated with the IOL implantation, and the consequent adhesion of cells to the lenses. In addition to the loss of performance due to these events, the IOL is liable to adhere to the surrounding tissues.
Also, investigations have been made to prevent the deposition of blood components by immobilizing heparin as a anticoagulant on the surface of the intraocular lens made of poly(methyl methacrylate), thereby providing a biocompatibility (Biomaterials, Vol. 10, pp. 511-516(Oct. 1989)). However, the heparin has an action of preventing a blood coagulation, but it suffers serious disadvantages that once fibrin is deposited from profuse bleeding and exudates, the lysis of the resulting fibrin becomes difficult.
Because of its desirable dynamic characteristics, silicone has also been used as the intraocular lens material, but because it has no effective functional groups on the surface, this material has the drawback that much time and labor are required for chemical modification on the lens surface, or other surface treatment. Furthermore, since silicone is water-and grease-repellent, such surface modifying methods tend to cause uneven coating or exfoliation of the coating, and it is difficult to cover the surface uniformly.
As a result of extensive investigation to overcome the above-mentioned conventional disadvantages, it has been found that the problems pointed out above can be neatly solved by immobilizing a substance having fibrinolytic activity on the surface of an intraocular lens. The present invention has been accomplished on the basis of the above finding.